1. Field of the Invention
This invention relates generally to switching power supply systems employing voltage regulating techniques for controlling voltages supplied to vacuum fluorescent displays (VFD) and more particularly to improved switching power supplies and voltage regulation techniques therefor which control brightness of individual sections of multisection VFDs.
2. Description of the Prior Art
In prior art multisectioned VFD systems, it is well-known that such displays may have several sections with a grid for each section requiring power wherein one section may house circuitry for five illustrating characters while another may house circuitry for only one character. Each character is formed from a combination of anode segments and if the character is considered a standard character usually it is composed of seven (7) anode segments.
If in a multisection system, e.g., there are four sections and the first three sections include two standard characters for display while the last includes one standard character and four non-standard characters, then the first three sections would in most instances, require from a power supply less anode and grid power per section than the last one because of the fewer anode segments. In most multisection display systems, section displays are generated sequentially from the first section to the last by energizing in turn each control grid while up-dating the anode segment information needed for the characters to be displayed. Since the grid loads may vary, but the grid voltage must remain substantially constant, various schemes have been devised to compensate for the variations.
Analog type pulsewidth modulator circuits using have been utilized to drive cup core type transformers. However, such systems have a disadvantage in that they cannot anticipate changing grid loads.
Other prior art systems have used microcomputers to control a switching power supply wherein the output voltage applied to the grids is sensed and converted to a digital equivalent voltage and fed back to the microcomputer for updating the grid voltages. Such systems provide effective control of grid voltages but usually an A/D port of the microcomputer is utilized which might otherwise be used for some other application and usually the associated components such as the transformers, even if it is a cup, core type, usually are large and bulky, consuming an inordinate amount of space.
Realizing problems such as the inconvenience of having to obtain a microcomputer with an A/D converter port, a search for various other means to effect controlling power to multisection displays was initiated. This search resulted in the improved system of the present invention.